My cat and dog get on well ( or did since my cat is now living with my parents because we're soon to relocate to the UK). My cat was 6 when we got Flo ( our cocker ), we had a stairgate to prevent Flo going up the stairs, and we put all of the cats good up on the laundrey bench and blocked off pups access to the litter tray. Our cat is a confident and very big tabby and with a few wacks ( didn't use claws) he soon made sure he was boss, once that was established fFlo and Lu ( cat) would sleep together, cuddle up and enjoy. Flo still wanted to play with Lu bit Lu usually wouldn't tolerate, although sometimes they would play chase, but only because Lu had Flo scared of him. Lu eventually came to treat visiting dogs the same way... Not running but standing his ground. I had cockers and cats growing up and when our cocker had pups our then cat would guard the pups and wouldn't let anyone but family near them, and when our cat had kittens our cocker would lie with them and tolerate the kittens trying to suckle her( must of hurt with their needle teeth and paws kneading).
So you can have great success, it just depends on the personalities, it seems like your cat is pretty confident if already sniffing visiting dogs, my vet did say it's best that the cat is older than the pup.
Good luck.